Automotive Air Conditioning Information Forum

I have a2006 GMC Sierra with a 5.3 I have no power going to the a/c compressor or high pressure switch I have replaced all fuses and relays plus replaced control panel freon levels are good had that checked low pressure switch has been jumped and have good ground on compressor and high pressure switch I can jump relay and engage clutch on compressor what am I missing ????

No signal from PCM to energize the relay.

No signal

Levicain82 wrote:No signal

Yes, the PCM either provides 12V or a ground to the coil in the relay and close the contact that energizes the compressor clutch coil.

Do these have compressor lockout coded into the PCM like many other GM's did? If the compressor starts cycling rapidly (due to low refrigerant) the PCM will shut it down until reset.

No compressor lock-outs on GM trucks- you most likely have a high side pressure transducer (3 wire) issue- located on high side line from compressor. Never jump this connector- it has a power supply input (5v), a ground, and a signal return that is proportional to system pressure- 0 to 5v return signal to ECM. So meter (DVM) each wire with a/c request and transducer plugged in to determine if you are good. I have seen broken wires at transducer, mice chewn wires underneath, and bad connectors.

You do have more than 47 psi static pressure in system as read by a gage set - right?

Yes pressures are correct. So it most likely a broke wire going to high pressure switch?? I know the ground is good on switch I just not sure where the other two wire go and how it check to find bad wire

Quit calling it a switch--if there are three wires it is a pressure transducer- sends variable pressure data to ECM to decide whether to turn off compressor for too high or too low pressure- can also command any auxiliary fans...Never try to "jumper" a three wire "switch"

I HAVE NOT JUMPED IT I don't have power to it or compressor that's what I'm trying to figure out I used a TESTING LIGHT to check ground and see if I had power which I have nothing at connector other then ground that what I'm trying to figure out is which wire does what and where the wires go to trace

Don't use a test light - use a DVM - digital volt meter- and check the three wires as referenced below- do you get signal confirmation?

black wire is ground
gray wire is 5volt reference or feed
red wire is the return voltage which is proportional to refrigerant pressure- should vary with pressure - 0-5vol

test with transducer plugged in and a/c requested with engine running or ignition on.